1. Technical Field
The present invention relates to an electrooptical device having a functional layer formed in openings of a bank, an electronic apparatus, and a method for producing an electrooptical device.
2. Related Art
An organic electroluminescent (EL) device is one type of electrooptical device. An organic EL device includes a light-emitting layer formed of a light-emitting material between an anode and a cathode. An example of a method for producing an organic EL device includes a step of ejecting an ink containing a light-emitting material into light-emitting regions on a substrate by ink jetting. The light-emitting regions are defined on the substrate by forming a bank for allowing predetermined portions to be filled with the ink using, for example, an organic material (such as acrylic resin).
The bank has, for example, track-shaped openings with long and short sides in the regions corresponding to the light-emitting regions. Such openings have a problem in that they are not readily filled with the ink inside arcs formed on the short sides because of poor ink wettability. This causes variations in the thickness of the ink ejected into the openings, thus preventing uniform light emission.
According to a method disclosed in JP-A-2005-158494, for example, two inorganic material layers (such as a silicon oxide film and a silicon nitride film) are formed under an acrylic resin bank such that the two layers are exposed in the form of steps (hereinafter referred to as a “bilayer bank”). The bilayer bank allows the openings of the bank to be filled with ink more readily. This known method improves ink wettability in the arc regions to form a film of uniform thickness in the openings.
In addition to the poor ink wettability inside the arcs formed on the short sides, as described above, the openings have a problem in that ink tends to spill over the long sides. This causes variations in the thickness of the ink ejected into the openings, thus preventing uniform light emission.
According to a method disclosed in JP-A-2003-187970, for example, an inorganic material layer (such as a silicon oxide film) is formed under an acrylic resin bank such that part of the layer is exposed. This layer allows the openings of the bank to be filled with ink more readily. This known method improves ink wettability to form a film of uniform thickness in the openings.
As the light-emitting regions are narrowed with increasing resolution, the size of the openings of the bank must be reduced accordingly. The bilayer bank, exposed on the sides of the openings in the width direction (on the long sides), can cause variations in the thickness of the ejected ink, depending on the accuracy of the amount of extension of the bilayer bank. This causes a problem in that light cannot be uniformly emitted (variations in light-emission characteristics). In addition, because the bilayer bank is formed in the form of steps, there is an increased amount of extension toward the light-emitting regions. This causes a problem in that the aperture ratio in the width direction of the openings is decreased.
As the light-emitting regions are narrowed (i.e., with increasing resolution), the curvature of the arcs is increased, and ink tends to recede from the arcs, particularly during a drying step. This makes it difficult to fill the light-emitting regions with ink. If the amount of ink is increased to ensure sufficient thickness, the ink tends to spill over the long sides. Thus, the contact angle with the ink differs between the long sides and the short sides, which therefore have variations in the thickness of the ink in the openings. This causes a problem in that light cannot be uniformly emitted (variations in light-emission characteristics).